This invention relates, in general, to polyethylene glycol (xe2x80x9cPEGxe2x80x9d) derivatives and, in particular, to PEG derivatives containing a diene functionality which may be used in a Diels-Alder reaction to prepare an array of PEG adducts.
PEG is the focus of considerable attention in the biotechnical and biomedical communities. It has been approved by the United States Food and Drug Administration for internal consumption and has been used in a variety of applications including, for example, drug compounding, surface modification (to provide protein and cell rejecting surfaces), hydrogels for cell encapsulation, drug delivery and wound covering, modification of small-molecule pharmaceuticals, and liposomes and micelles for drug delivery. These and other applications for PEG are described in detail in the literature. See, for example, Zalipsky, S., Bioconjugate Chem. 6, 150-165 (1995); Herman, et al., Journal of Bioactive and Compatible Polymers, 10, 145-187 (1995); Poly(ethylene glycol) Chemistry. Biomedical and Biotechnical Applications, J. M. Harris, Editor, Plenum, New York (1992); and Poly (ethylene glycol) Chemistry and Biological Applications, J. M. Harris and S. Zalipsky, editors, ACS Symposium Series: American Chemical Society: Washington, D.C. (1997).
For use in these various applications, an xe2x80x9cactivatedxe2x80x9d form of PEG, commonly referred to as a PEG derivative is used. Typically, PEG derivatives contain at least one electrophilic center available for reaction with nucleophilic centers of biomolecules (e.g., lysine, cysteine and like residues of proteins) or surfaces (e.g., aminated glass). For example, Royer describes the preparation of PEG acetaldehyde for attaching PEG to enzymes and other proteins in U.S. Pat. No. 4,002,531. Harris et al. describe the preparation of PEG propionaldehyde for linking or tethering molecules to organic or polymer surfaces in water in U.S. Pat. No. 5,252,714. Other PEG derivatives for these and other applications are described in S. Zalipsky, Advanced Drug Delivery Reviews, 16, 157 (1995); K. Nilsson and K. Mosbach, Methods in Enzymology, 104, 56 (1984); C. Delgado, G. E. Francis, and D. Fisher, in xe2x80x9cSeparations Using Aqueous Phase Systems,xe2x80x9d D. Fisher and I. A. Sutherland, Eds., Plenum, London, 1989, pp. 211-213; M. B. Stark and J. K. Holmberg, Biotech. Bioeng., 34, 942 (1989); J. M. Harris and K. Yoshinaga, J. Bioact. Compat. Polym., 4, 281 (1989); H. Walter, D. E. Brooks, and D. Fisher (Editors), xe2x80x9cPartitioning in Aqueous Two-Phase Systems,xe2x80x9d Academic Press, Orlando, Fla., 1985; D. Fisher and I. A. Sutherland (Editors), xe2x80x9cSeparations Using Aqueous Phase Systems: Applications in Cell Biology and Biotechnology,xe2x80x9d Plenum, London, 1989.
While a number of PEG derivatives have been identified and some are now commercially available, interest remains for new PEG derivatives that possess novel properties. In particular, there is an interest in new PEG derivatives which upon further chemical modification are useful in biomedical applications and permit the synthesis of new polymers (e.g., copolymers, homopolymers, and optically active polymers).
Among the objects of the present invention, therefore, is the provision of PEG derivatives which upon further chemical modification are useful in biomedical applications, permit the synthesis of new polymers (e.g., copolymers, homopolymers and optically active polymers), are optionally stable in water, selectively react with functional groups such as amines and thiols, are capable of efficiently linking or tethering molecules to organic or polymer surfaces in water by use of PEG derivatives, or may be used as intermediates in the preparation of compositions possessing such properties.
Briefly, therefore, the present invention is directed to a PEG derivative having the formula
Xxe2x80x94(xe2x80x94CH2CH2Oxe2x80x94)nxe2x80x94(xe2x80x94CH2CH2Yxe2x80x94)mxe2x80x94R1xe2x80x83xe2x80x83(1)
wherein
m is a cardinal number (that is, 0 or at least 1);
n is at least 1,
R1 is a diene moiety selected independently from R2,
R2 is a diene moiety selected independently from R1,
X is hydroxyl, xe2x80x94YR2, optionally substituted hydrocarbyloxy, or heteroaryloxy; and
Y is oxygen, sulfur or xe2x80x94NHxe2x80x94.
The present invention is further directed to a process for the preparation of a cyclic product. The process comprises reacting a PEG derivative containing a diene moiety with a dienophile in a Diels-Alder reaction.
Other objects will be in part apparent and in part pointed out hereinafter.
In accordance with the present invention, a class of PEG derivatives having a diene moiety have been discovered which, upon further chemical modification, are of interest in connection with various biotechnical and biomedical applications. In addition, some of these PEG derivatives permit the synthesis of new polymers (e.g., copolymers, homopolymers and optically active polymers).
The PEG derivatives of the present invention have the formula
Xxe2x80x94(xe2x80x94CH2CH2Oxe2x80x94)nxe2x80x94(xe2x80x94CH2CH2Yxe2x80x94)mxe2x80x94R1xe2x80x83xe2x80x83(1)
wherein m, n, R1, X and Y are as previously defined. In one embodiment, X is xe2x80x94YR2 and R1 and R2 are the same diene moieties. For example, R1 (and R2 when present) may be a substituted or unsubstituted hydrocarbyl radical containing a conjugated diene. Alternatively, R1 (and R2 when present) may be a substituted or unsubstituted heterocyclic radical. In any event, R1 (and R2 when present) is preferably in, or capable of adopting a cisoid conformation. More preferably, R1 (and R2 when present) is
xe2x80x94(CH2)tCHxe2x95x90CHxe2x80x94CHxe2x95x90CR3R4xe2x80x83xe2x80x83(2) 
wherein
p is at least 1;
R3 and R4 are independently hydrogen, alkyl or aryl;
R5 and R 55 are independently alkyl, alkenyl, alkynyl, aryl or heteroatomic;
a is 0-2, preferably 0 or 1, more preferably 0;
b is 0-2, preferably 0 or 1, more preferably 0;
t is a natural number greater than zero;
v is 0-3, preferably 0 or 1, and more preferably 0; and
w is 0-4, preferably 0 or 1, and more preferably 0.
In one embodiment of the present invention, n is at least about 20, more preferably is at least about 30, and still more preferably about 30 to about 50. In general, it is preferred that n be less than 500, and more preferably less than about 200. In addition, m is preferably no greater than 5, more preferably no greater than 3, and still more preferably 0.
In general, therefore, in preferred PEG derivatives of the present invention n is at least about 20, m is 0-5, X is hydroxyl, alkoxy (such as methoxy) alkenyloxy, alkynyloxy, or aryloxy (such as benzyloxy), Y is oxygen (if m is at least 1), t is 1, and w is preferably 0. In one preferred embodiment of the present invention R1 (and R2 when present) is
xe2x80x94(CH2)tCHxe2x95x90CHxe2x80x94CHxe2x95x90CR3R4
in the trans configuration, and R3 and R4 are preferably lower alkyl or hydrogen (more preferably hydrogen). In other preferred embodiments, R1 (and R2 when present) corresponds to one of structures 3 to 6, and R5 (if present) or R55 (if present) are/is preferably hydrogen or lower alkyl.
The PEG derivatives of the present invention advantageously serve as the diene in a Diels-Alder type cycloaddition reaction with a dienophile. The dienophile for this reaction is preferably a substituted or unsubstituted alkene, alkyne or heteroatomic. In general, dienophiles bearing electron-withdrawing groups such as carbonyl, carboxylate, sulfonyl, sulfonate, cyano, halogen, nitro, trihaloalkyl groups undergo the Diels-Alder reaction with facility. Preferred dienophiles include substituted alkenes such as acrolein, acrylic acid, benzoquinone, maleic anhydride, acrylonitrile, and vinyl ketones such as methylvinyl ketone. Preferred dienophiles also include substituted alkynes such as dicyanoacetylene and esters of acetylenedicarboxylic acid. Heteroatomic dienophiles are also preferred such as the iminourethanes and esters of azodicarboxylic acid.
Diels-Alder reactions are typically carried out in an organic solvent, typically an aprotic organic solvent such as tetrahydrofuran or toluene, or in water at or above room temperature. In general, the reaction is carried out with a molar excess of dienophile with molar ratios of dienophile to diene of about 2:1 being typically preferred.
The term xe2x80x9cdiene moietyxe2x80x9d is defined to mean a radical or functional group which enables a compound to react with a dienophile in a Diels-Alder reaction in somewhat the same manner as a conjugated diene reacts with an alkene in a Diels-Alder reaction. Such diene moieties include, for example, conjugated dienes and certain heterocyclic radicals.
The xe2x80x9chydrocarbonxe2x80x9d and xe2x80x9chydrocarbylxe2x80x9d moieties described herein are organic compounds or radicals consisting exclusively of the elements carbon and hydrogen. These moieties include alkyl, alkenyl, alkynyl, and aryl moieties. These moieties also include alkyl, alkenyl, alkynyl, and aryl moieties substituted with other aliphatic or cyclic hydrocarbyl groups, and include alkaryl, alkenaryl and alkynaryl. Preferably, these moieties comprise 1 to 20 carbon atoms.
The alkyl groups described herein are preferably lower alkyl containing from one to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight, branched chain or cyclic and include methyl, ethyl, propyl, isopropyl, butyl, hexyl and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The alkenyl groups described herein are preferably lower alkenyl containing from two to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight or branched chain and include ethenyl, propenyl, isopropenyl, butenyl, isobutenyl, hexenyl, and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The alkynyl groups described herein are preferably lower alkynyl containing from two to six carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight or branched chain and include ethynyl, propynyl, butynyl, isobutynyl, hexynyl, and the like. They may be substituted with aliphatic or cyclic hydrocarbyl radicals.
The aryl moieties described herein are carbocyclic aromatic moieties, preferably containing from 6 to 20 carbon atoms. They may be substituted with the various hydrocarbyl, substituted hydrocarbyl or heteroatomic moieties defined herein. Phenyl and substituted phenyl are the more preferred aryl.
The heteroatomic moieties described herein are compounds or radicals which contain one atom other than carbon and hydrogen such as nitrogen, and preferably no more than about 20 atoms, usually no more than 5 or 6 atoms. The heteroatomic moiety may be a single atom other than carbon and hydrogen, e.g., a halogen atom, a substituted heteroatom such as hydroxyl or amino, a straight or branched chain containing a heteroatom, or heterocyclic. The heteroatomic moieties may be substituted with hydrogen, hydrocarbyl, heterosubstituted hydrocarbyl or hetero-atom containing substituents with the hetero atoms being selected from the group consisting of nitrogen, oxygen, silicon, sulfur, and halogens. These heteroatomic moieties include hydroxyl; lower alkoxy such as methoxy, ethoxy, butoxy; halogen such as chloro; or fluoro; ethers; esters; heteroaryl such as furyl; alkanoxy; acyl; acyloxy; nitro; amino; and amido.
The heterocyclic moieties described herein are cyclic heteroatomic compounds or radicals, preferably containing a total of 5 to 20 atoms, usually 5 ring atoms, and at least one ring atom other than carbon. The heterocyclic moiety may be heteroaryl, that is, a heterocyclic moiety analogous to the aromatic compounds or radicals, and include, for example, furyl and the like. The heterocyclic moieties may be substituted with hydrocarbyl, heterosubstituted hydrocarbyl or hetero-atom containing substituents with the hetero-atoms being selected from the group consisting of nitrogen, oxygen, silicon, phosphorous, boron, sulfur, and halogens. These substituents include hydroxyl; lower alkoxy such as methoxy, ethoxy, butoxy; halogen such as chloro or fluoro; ethers; acetals; ketals; esters; heteroaryl such as furyl; alkanoxy; acyl; acyloxy; nitro; amino; and amido.
The substituted hydrocarbyl moieties described herein are hydrocarbyl moieties which are substituted with at least one atom other than carbon and hydrogen, including moieties in which a carbon chain atom is substituted with a heteroatom such as nitrogen, oxygen, silicon, phosphorous, boron, sulfur, or a halogen atom. These substituents include hydroxyl; lower alkoxy such as methoxy, ethoxy, butoxy; halogen such as chloro or fluoro; ethers; esters; heteroaryl such as furyl; alkanoxy; acyl; acyloxy; nitro; amino; and amido.
The acyl moieties and the acyloxy moieties described herein contain hydrocarbyl, substituted hydrocarbyl or heteroaryl moieties. In general, they have the formulas xe2x80x94C(O)G and xe2x80x94OC(O)G, respectively, wherein G is substituted or unsubstituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylthio or heteroaryl.